Method of preparing diacetyl



Patented Jan. 31, 1939 UNITED STATES PATENT OFFICE METHOD OF PREPARING DIACETYL No Drawing. Application December 23, 1936, Serial No. 117,384

7 Claims.

and the process has not been commercially practical.

The preparation of methyl vinyl ketone (2-butenone)CHaCOCH=CHz from vinyl acetylene has been disclosed in U. S. Patent 1,896,161.

According to this process vinyl acetylene is passed thru an aqueous acid solution in the presence of a hydration catalyst, for example, a mercuric salt 20 such as mercuric sulfate, whereby to hydrate the triple bond in the vinyl acetylene to form an unsaturated ketone. Several variations of this process are disclosed.

In carrying out this process it was noted that there was some tendency for reduction of the catalyst to take place, particularly where a mercuric salt was used and that certain by-products resulted. Among the by-products separated was one boiling above methyl vinyl ketone. Its boil- 30 ing point was noted but its chemical composition was not definitely ascertained. It has now been found, however, that this product is diacetyl.

In the -U. S. Patent 1,896,161 emphasis was placed upon the production of methyl vinyl ke- 35 tone but while still operating according to the conditions there given, it is possible to so select conditions that large portions of diacetyl are produced along with the methyl vinyl ketone.

It is an object of this invention to prepare 40 diacetyl from a readily obtainable raw material,

methyl vinyl ketone, by a new and economical process. It is afurther object of this invention to prepare diacetyl in large yields. Other objects will appear hereinafter.

i5 It has now been found that the formation of diacetyl in the production of methyl vinyl ketone is the result of the oxidation of the unsaturated ketone by means of the mercury salts and that it may not only be carried out simultaneously 50 with the hydration of the methyl vinyl acetylene,

but that it may also be effected as the subsequent step. Thus, when methyl vinyl ketone is passed into contact with a solution of a mercury salt in an aqueous acid medium of the type so described hereinafter. it has been found that the methyl vinyl ketone is converted in large yields to diacetyl.

For the purpose of the hydration described in U. S. Patent 1,896,161, the following acids were found especially valuable; sulfuric acid, acetic .5 acid, phosphoric acid, sulfo-acetic acid, mono-, diand trichloroacetic acid, and almost any acid which, in the concentrations applied, did not result in charring or decomposition of the desired products. It has been found that these same acids may be applied in the process of oxidizing the methyl vinyl ketone to diacetyl and that the same wide concentration limits may be used. A preferred, concentration range is about to 30% of sulfuric acid or its equivalent. 15

In the previous patent several metals were described as .functioning catalytically for the hydration, but for the purpose of this invention which involves the oxidation, mercuric salts alone have been found especially adapted for use, altho the same wide variations in concentration are still applicable. If the process is carried out continuously it has been found preferable to employ an acid solution containing about 10% to 15% HgS04.

An important feature of the present invention is a heating of the reaction mixture for some time at temperatures up to 100. C. if the reaction is carried out in a batch manner, or if continuous, that the same effect be obtained by recirculating the unoxidized reactants, separating only that portion of the eiiluent gas which has been converted to diacetyl. Thus, in Example 1 of the previous U. S. Patent 1,896,161, a mixture was prepared containing mercuric sulfate and sulfuric acid, into which was passed vinylacetylene, which was then aged until reaction was complete at 35 0., giving a crude methyl vinyl ketone. Careful fractionation of this product also gives small quantities of diacetyl which, as pointed out above, boils slightly higher than the methyl vinyl ketone. Upon varying the process of Example 1, however, within the limits of the previous patent by carrying out the aging at 90 C. or above instead of at 35 C., the diketone, that is, diacetyl, becomes the principal product of the reaction. According to the present process methyl vinyl ketone is used as the starting material and a similar aging at 90 C. or even up to 100 C. is carried out in the presence of the mercury catalyst to produce the same product, diacetyl.

For the purpose of indicating preferred methods for carrying out the present invention, the following examples are given. It is to be understood, however, that these examples are intended to be illustrative only and that they are not to be construed as limiting the invention:

Example 1 One mol. of methyl vinyl ketone gms.) is added to a vessel containing 1200 grams of mercuric sulfate,- 1500 grams of sulfuric acid, and 6500 grams of water. The vessel is closed and while held at C. to C., the reaction mass is agitated for six hours. At the end of this period, the reaction mass is distilled and the diacetyl separated from the aqueous distillate by extraction or salting out with calcium chloride.

In the above example, equivalents may be substituted, for example, dilute sulfuric acid may be used with a suitable adjustment of the water content, or mercuric oxide may be used in place of the sulfate with a corresponding increase in the quantity of sulfuric acid and, in general, the variations of the process discussed above may be applied. This example is included particularly for the purpose of illustrating preferred conditions of operation for the batch process. By comparison with U. S. Patent 1,896,161, it will be seen that a similar acid mercury solution may be used, saturating at lower temperature with vinylacetylene, which will be converted to methyl vinyl ketone and then may be subsequently oxidized'as described above without isolation.

Example 2 A catalyst solution similar to that described in Example 1 is allowed to flow down thru a packed column heated to 100 C. in a countercurrent to a stream of gaseous methyl vinyl ketone. The efiiuent gases are continuously condensed and separated, returning the unreacted 'butenone to the reactor and isolating the diacetyl.

It will be observed that during these various examples, a part of the mercury is consumed by reduction, that is to say, rendered ineffective as a catalyst for this process. In a continuous process, it is necessary to provide for continual replacement of a part of the mercuric solution and for reoxidation of the mercury to the mercuric state before returning it to the reaction vessel so as to maintain the concentration of mercuric salt substantially constant in the acid catalytic solution.

Example 3 Example 1 is repeated, but using twice the quantity of sulfuric acid described above. In this case, the oxidation is somewhat more rapid and the liberation of the product upon distillation of the oxidized mass takes place more readily.

Example 4 Example 1 may be repeated using an oxidation solution composed of 800 grams of mercuric oxide, 2000 grams of phosphoric acid and 4000 grams of water with similar results.

The above process provides a convenient method for synthesizing diacetyl from a readily available raw material, methyl vinyl ketone. Altho previous methods have been described for synthesizing diacetyl, they do not compare in cost and commercial practicability with the present one.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof and therefore it is not intended to be limited except as indicated in the appended claims.

I claim:

1. The method of preparing diacetyl from methyl vinyl ketone by oxidizing the methyl vinyl ketone by means of mercuric salts, which comprises carrying out the oxidation by bringing the methyl vinyl ketone into contact with the mercuric salts and continuing the treatment so that a major proportion of the methyl vinyl ketone is converted to diacetyl.

2. The method of preparing diacetyl which comprises heating methyl vinyl ketone at a temperature of about 80 C. to about 100 C. for a substantial period in the presence of an aqueous acid solution of a mercuric salt.

3. The method of preparing diacetyl which comprises heating methyl vinyl ketone at a temperature of about 80 C. to about 100 C. for about six hours in the presence of an aqueous acid solution of a mercuric salt of the group consisting of mercuric sulfate, mercuric acetate, mercuric phosphate, mercuric sulfoacetate, mercuric monochloracetate, mercuric dichloracetate, and mercuric trichloracetate.

4. The process of preparing diacetyl which comprises continuously passing methyl vinyl ketone into contact with an aqueous acid solution of a mercuric salt maintained at a temperature of about 80 C. to about 100 C., continuously separating from the eiiluent gases diacetyl, and continuously returning the unreacted methyl vinyl ketone to the catalyst zone.

5. The process of preparing diacetyl which comprises continuously passing 1" thyl vinyl ketone into contact with an aqueous acid solution of a mercuric salt of the group consisting of mercuric sulfate, mercuric acetate, mercuric phosphate, mercuric sulfoacetate, mercuric monochloracetate, mercuric dichloracetate, and mercuric trichloracetate maintained at a temperature of about 80 C. to about 100 C., continuously separating from the efiluent gases diacetyl, and continuously returning the unreacted methyl vinyl ketone to the catalyst zone.

6. The process of claim 5 in which the aqueous acid solution is an about 15% to about 30% solution of sulfuric acid and in which the mercuric salt is mercuric sulfate which is present in a concentration equal to about 10% to about 15% of the acid solution.

'7. The process of preparing diacetyl, which comprises continuously passing methyl vinyl ketone into contact with an aqueous catalyst solution consisting of about 12 parts of mercuric sulfate, about 15 parts of sulfuric acid, and about 65 parts of water maintained at a temperature of about 100 C., continuously separating from the eiliuent gases diacetyl, continuously returning the unreacted methyl vinyl ketone to the catalyst zone, continuously drawing off a portion of the catalyst solution, continuously reoxidizing the mercury therein to the mercuric state, and continuously returning the reoxidized solution to the main body of catalyst.

ALBERT S. CARTER. 

